Clarify 2FA troubleshooting and recovery options

What does this MR do and why?

Moved the two-factor authentication (2FA) Troubleshooting and Recovery options sections to a new page.

Reason

This should make the self-help information for 2FA issues more discoverable to customers and users.

Other considerations

From the linked issue: Consider other options, such as raising the profile of 2FA on key landing pages such as:

• https://docs.gitlab.com/ee/topics/set_up_organization.html
• https://docs.gitlab.com/.

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Related issue: #468894